What to do with pre cat and after cat 02 sensors

[L31MaxExpress]

that is weird I have only seen 1 305 vortec truck it was a 99 gmc K-1500 classic it only had 3 o2 sensors on it 2 up stream and 1 post cat

I have never see one without the 3rd upstream sensor. Even the S10s have them and they are hard to get at in a S10 chassis.

 

[99xcss4]

we have 2 98 gmc jimmy one has a mini pre cat the other one dose not both of them no longer have the main cat any more have not seen a pre cat sensor on either of them dose not mean it is not there maybe it is just weird gm stuff who really knows

 

[L31MaxExpress]

we have 2 98 gmc jimmy one has a mini pre cat the other one dose not both of them no longer have the main cat any more have not seen a pre cat sensor on either of them dose not mean it is not there maybe it is just weird gm stuff who really knows

Agreed on GM doing weird stuff, looked up under a 5.7L powered Express van in the wrecking yard a few months back. No 02s and no cats, it was built that way too. Grabbed the VIN and decoded it. Had a pretty nice looking 2.5" to single 3" Y-pipe on its as well. The pipes ahead of the Y were 2.5 off the manifolds and flared out to dual 3". The Y itself was dual 3" to single 3".

I wish the 0411 had been there, I wanted a copy of the factory open loop, catless tune.

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[99xcss4]

I have seen some thing close to that on a 97 C-1500 extend cab 3rd door short bed 305 with leather interior that a friend of mine use to have it had no cat and to my best memory no down stream o2 sensor and it was factory

 

[L31MaxExpress]

I have seen some thing close to that on a 97 C-1500 extend cab 3rd door short bed 305 with leather interior that a friend of mine use to have it had no cat and to my best memory no down stream o2 sensor and it was factory

I know for a 100% fact that the National Parks and Forest service had trucks available to them without catalytic converters. Without catalytic converters there is not much reason for any 02 sensors. Those trucks used the leaded fuel export exhausts.

 

[supspt454]

That's right. The single catalyst Vortec smaller engines do have 3 upstream sensors that sample left, right and combined pre catalyst. Then a single downstream post cat sensor.

I was made aware a bit ago, as I thought all Vortecs were dual pipes, dual catalyst, into a single muffler and tailpipe.

@supspt454 have your tuner remove the 3rd O2 sensor PID in the PCM. Use 2 up and 1 down sensors. Then cover the pigtail, maybe even cut the sensor side wires and cap them off to protect the pins in the pigtail.

I have HP Tuners and plan to learn how to do this myself. The truck will not have any cats. So I guess my question should be can the bank 1 sensor 2 (combined pre cat) be deleted along with bank 1 sensor 3 (post cat).

 

[BeXtreme]

I have HP Tuners and plan to learn how to do this myself. The truck will not have any cats. So I guess my question should be can the bank 1 sensor 2 (combined pre cat) be deleted along with bank 1 sensor 3 (post cat).

With no cats and an 0411, you will remove the codes for all O2's except for Bank1 Sensor 1 and Bank 2 Sensor 1. Everything else is only used for cats and emissions. You will also want to disable all of the catalyst protection tables, since you don't want it to start pulling power or overfueling to try to protect cats that aren't there.

 

[supspt454]

With no cats and an 0411, you will remove the codes for all O2's except for Bank1 Sensor 1 and Bank 2 Sensor 1. Everything else is only used for cats and emissions. You will also want to disable all of the catalyst protection tables, since you don't want it to start pulling power or overfueling to try to protect cats that aren't there.

Excellent. Just what I wanted to hear. Thanks a lot for the info. I kind of figured this, but being new to EFI tuning, just wanted to be sure I was thinking correct.

 

[L31MaxExpress]

With no cats and an 0411, you will remove the codes for all O2's except for Bank1 Sensor 1 and Bank 2 Sensor 1. Everything else is only used for cats and emissions. You will also want to disable all of the catalyst protection tables, since you don't want it to start pulling power or overfueling to try to protect cats that aren't there.

Do not agree on removing catalyst overheat mode. That is there to protect your pistons and exhaust valves as well. The added fuel is needed to cool them when the engine runs hard for a long period of time. It only richens it to about 11.8:1 at the most.

I will add that I run a fairly aggressive PE air/fuel for E10, around 12:1 at peak torque and 12.6:1 at peak HP. When it shifts to catalyst overheat it richens up the air/fuel and I pull 2-3* of timing out of it in the AFR compensation spark table at the richer commanded AFR in catalyst overheat mode. With the the stoich value at 14.1, I end up about 11.2:1 in catalyst overheat. Does not make a 2-3 HP difference to protect the pistons and valves as well as help prevent detonation when things really heat up.

 

[supspt454]

Do not agree on removing catalyst overheat mode. That is there to protect your pistons and exhaust valves as well. The added fuel is needed to cool them when the engine runs hard for a long period of time. It only richens it to about 11.8:1 at the most.

I will add that I run a fairly aggressive PE air/fuel for E10, around 12:1 at peak torque and 12.6:1 at peak HP. When it shifts to catalyst overheat it richens up the air/fuel and I pull 2-3* of timing out of it in the AFR compensation spark table at the richer commanded AFR in catalyst overheat mode. With the the stoich value at 14.1, I end up about 11.2:1 in catalyst overheat. Does not make a 2-3 HP difference to protect the pistons and valves as well as help prevent detonation when things really heat up.

I defiantly have a lot to learn lol. Oklahoma does not have inspections, I say I won't be running cats, but I am still thinking if I should put high flow cats on or not. Most likely not, depends on if this muffler will be too loud.